Observation of temperature profiles by RASS

Transcription

Atmospheric
Measurement
Techniques
Discussions
T. V. Chandrasekhar Sarma , P. Srinivasulu , and T. Tsuda
2
1
Correspondence to: T. V. Chandrasekhar Sarma ([email protected])
Published by Copernicus Publications on behalf of the European Geosciences Union.
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Received: 3 May 2012 – Accepted: 7 June 2012 – Published: 29 June 2012
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Observation of
temperature profiles
by RASS
T. V. Chandrasekhar
Sarma et al.
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Abstract
Introduction
Conclusions
References
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National Atmospheric Research Laboratory (NARL), Gadanki, 517 112 AP, India
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Research Institute for Sustainable Humanosphere (RISH), Kyoto University,
Uji 611 0011, Kyoto, Japan
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Preliminary observation of temperature
profiles by radio acoustic sounding
system (RASS) with a 1280 MHz lower
atmospheric wind profiler at Gadanki,
India
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This discussion paper is/has been under review for the journal Atmospheric Measurement
Techniques (AMT). Please refer to the corresponding final paper in AMT if available.
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Atmos. Meas. Tech. Discuss., 5, 4447–4472, 2012
www.atmos-meas-tech-discuss.net/5/4447/2012/
doi:10.5194/amtd-5-4447-2012
© Author(s) 2012. CC Attribution 3.0 License.
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A UHF wind profiler operating at 1280 MHz has been developed at NARL for atmospheric studies in the planetary boundary layer. In order to explore application of radio
acoustic sounding system (RASS) technique to this profiler, a suitable acoustic attachment was designed and preliminary experiments were conducted on 27–30 August
2010. Height profiles of virtual temperature, Tv , in the planetary boundary layer were
derived with 1 µs and 0.25 µs pulse transmission, corresponding to a height resolution
of 150 m and about 40 m, respectively. Diurnal variation of Tv is clearly recognized, and
perturbations of Tv are also seen in association with a precipitation event. Simultaneous
profiles obtained from the MST Radar-RASS and an onsite 50 m tower demonstrate the
capability to continuously profile the atmospheric temperature from near the ground to
upper tropospheric altitudes.
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1 Introduction
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Ground based remote profiling of atmospheric parameters in the boundary layer is
important in the research and operational applications related to industrial pollution
dispersion, heat and water vapour flux, air traffic control, satellite launch vehicle sites,
nuclear plant installations etc. Measurement of height profiles of wind velocity, temperature and water vapour in the boundary layer have been done using a sodar, a lidar,
a wind profiler, and so on. In particular, wind profilers with RASS have been developed for continuously monitoring wind velocity and virtual temperature regardless of
weather conditions. May and Wilczak (1993) used a 915 MHz profiler-RASS located
near Denver, Colorado to obtain height profiles of wind and virtual temperature in the
boundary layer and used them to study the evolution of the nocturnal boundary layer.
Using a similar RASS, Angevine et al. (1993) obtained virtual heat flux measurements
in the convective boundary layer. They also compared these derivations with the flux
measurements from aircraft and found consistency between the measurements as well
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Observation of
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as theory. A study of the conditions under which RASS derived heat fluxes are reliable was done by Furger et al. (1995). Angevine et al. (1998) compared the wind
and temperature measurements from a RASS to those from a 450 m tower. Westwater
et al. (1999) compared the temperature profiles from a boundary layer RASS with those
from a scanning radiometer. May (1999) studied the structure and thermodynamics of
gust fronts over an oceanic site using 920 MHz wind profiler-RASS.
Recently UHF wind profilers working in the upper UHF band (at 1280 MHz) were
developed at NARL. Two versions were developed for planetary boundary layer studies. The first one has a transmission peak power of 800 W and an 8 × 8 rectangular
patch phased active antenna array of size 1.4 m × 1.4 m (Srinivasulu et al., 2011). This
system was operated for some time at NARL in Gadanki (13.46◦ N, 79.17◦ E), and it
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was later moved to a location near Chennai (12.55 N, 80.12 E). A second system with
a transmission power of 1.2 kW and a 16×16 rectangular patch active antenna array of
size 2.8 m × 2.8 m has been in operation at Gadanki (Srinivasulu et al., 2012). Technical details of these radar systems are reported in Srinivasulu et al. (2006). These wind
profilers have a range coverage starting from almost near ground (∼100 m) to about
3 km and 5 km for low and high power systems, respectively.
RASS technique was applied to the MST radar of NARL, operated at 53 MHz, and
virtual temperature profiles were obtained in the height range of 1.5 km to about 14 km
in altitude (Chandrasekhar Sarma et al., 2008, 2011). Height coverage of Tv profiles during some experiments reached altitudes of about 19 km and beyond (Chandrasekhar Sarma, 2011). With the aim of extending the temperature profiling capability
at NARL downwards below 1.5 km the RASS technique was applied to the second UHF
wind profiler. For this purpose, acoustic attachments were constructed. Preliminary experiments were carried out during 27–30 August 2010 along with MST-Radar RASS at
Gadanki. This paper describes the system and presents preliminary results.
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2.1 System description of lower atmospheric wind profiler (LAWP) developed
at NARL
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A RASS consists of a wind profiler and a collocated acoustic source (cf. May et al.,
1990). The wind profiler is used to measure the Doppler shift due to the acoustic excitation which is proportional to the line of sight apparent sound speed in the direction of
the antenna beam. The frequency of the acoustic excitation is chosen so that the wave
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2.2 RASS for LAWP
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The antenna array of LAWP consists of 256 rectangular patch elements at a 0.73λ
◦
separation. Consequently, the beamwidth is 5 , first sidelobe level is 16 dB below the
main lobe and the grating-lobe free beam steering range is ±20◦ . Each of the antenna
elements is fed by a solid-state TR module generating a peak power of 10 W. The
TR module is capable of transmitting a pulsed waveform of duty cycle up to 10 %. The
range of pulse widths of transmission is 0.25 µs to 8 µs. Table 1 shows the specifications
of the wind profiler system.
Figure 1 shows photographs of the two sets of LAWP. For the smaller LAWP, the
64 antenna elements with a surrounding ground-clutter fence are installed on top of
a transportable aluminium cubicle (Srinivasulu et al., 2011). The associated TR modules are attached on the ceiling of the cubicle in order to minimize wiring between the
module and antenna elements. Other electronics and a radar control computer are
installed in the enclosure below.
The 256 element system was housed in a room in a concrete building of NARL with
the antenna kept on the rooftop and TR modules projecting into the room below. Such
an arrangement provides an enclosed space that can be environmentally controlled so
as to provide ideal temperature, humidity and dust free conditions for efficient performance of radar electronics. Further, the cable transmission losses can be minimised.
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2 Experimental set-up
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γR
kh =
M
(2)
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where q (kg kg−1 ) is the specific humidity which is normally the highest near the surface
and decreases exponentially with altitude.
As the radar wavelength of LAWP is 0.23 m corresponding to the 1280 MHz fre−1
quency, the acoustic frequency would be 2978.5 Hz for the acoustic speed of 349 m s
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(at 30 C). Taking a temperature measurement range of 45 C on the ground to about
−10 ◦ C at around 7 km altitude, the acoustic frequency range required would be between 3051 Hz and 2775 Hz. Commercial off-the-shelf components were used for the
development of acoustic transmitter due to their easy availability.
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Tv = (1 + 0.608q)T
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where γ = 1.4, R = 8314.472 J K−1 kmol−1 and M = 28.964 kg kmol−1 are ratio of specific heat at constant pressure to specific heat at constant volume, universal gas constant and mean molecular weight of dry air, respectively. For a dry atmosphere kh
works out to be 20.047. RASS determines ambient virtual temperature Tv , which is defined as the temperature that dry air would have if its pressure and density were equal
to those of a given sample of moist air. Absolute temperature T and Tv are related as,
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The constant kh (J K−1 kg−1 ) in Eq. (1) is given by
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number of refractive index perturbations induced in the atmosphere along the radar
beam is twice the radar RF transmission wave number. Such a relationship is essential
to obtain Bragg scatter from the propagating acoustic wavefronts. The radar measures
the wind velocity and the propagation speed of acoustic wavefronts, Ca (ms−1 ), which
is related to ambient temperature T (K),
2
Ca
.
(1)
T=
kh
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The acoustic transmitter consists of a PC-based signal generation, pre-amplifier,
power amplifier, compression driver and acoustic horn. Two types of compression
drivers were used: high power (JBL 2450H) and lower power (Ahuja AU-60). The
JBL2450H driver is an 8 Ohm device with a 150 Wrms continuous output rating for
frequencies above 1 kHz. The AU-60 is a 16 Ohm device with a 60 Wrms and 90 W
peak rating and 132 dB SPL at 1 m. The acoustic horn is also made by Ahuja Radios
(Ahuja WFB) and is suitable for direct use with AU-60; these products are meant for
public address systems. To allow mounting of JBL2450H, the horn was modified to
accommodate the larger throat diameter of this compression driver.
Figure 2 shows the horn arrangement. Each of the horns was mounted in a mild
steel frame so that it would point upwards and could be deployed in the field. It is an
exponential horn folded twice in a reflex design as shown in Fig. 2a. The horn is made
of aluminium with a mouth diameter of 18 inch (45.7 cm) and has lower cutoff frequency
of 190 Hz. It can accommodate a compression driver of outer throat diameter 3.5 cm.
This horn was chosen due to its broad frequency response, easy local availability, low
cost and suitability for outdoor use. The AU-60 is a suitable driver for direct use with
the WFB. Further it is also made of aluminium and is suitable for continuous outdoor
use as the WFB. For use with JBL2450H the horn was modified as shown in Fig. 2b.
In this arrangement the driver was mounted at the second fold of the horn where the
diameter of the horn is greater than that of the throat diameter of the driver using a poly
vinyl chloride (PVC) pipe and PVC coupling. The portion of the reflex horn below that
diameter was removed. In both of the configurations, three holes were drilled at the
bottom of the horn to allow drainage of rainwater.
The signal generation is based on a notebook personal computer for flexibility in
waveform design and compact footprint. A MATLAB programme was generated which
would compute the voltages for a chirped waveform between the low and high frequencies of the acoustic excitation required to satisfy Bragg scatter condition between the
expected temperature extremes. The file was stored in .wav format and was played
using commonly available media player programmes like the Windows Media Player,
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Real Player or the VLC Media Player. The notebook PC has a stereo headphone output from which the voltages corresponding to the digital data being played out on the
PC is available. This output is connected to the input of a Sonifex RB-UL4 unbalanced
to balanced converter preamplifier. The pre-amplifier converts the two single ended inputs to two differential outputs along with ground in the XLR connector format, suitable
for driving the voltages over long distances up to the power amplifier and also providing
common mode noise rejection. The outputs of the preamplifier form inputs to Crown
CL2 power amplifier. The compression drivers are driven from the outputs of the power
amplifier. The electronics are kept inside the room. The acoustic transmission system
described in the previous section was tested at a 3 kHz tone for checking the power
output. With the JBL2450H the maximum SPL that could be achieved was 128 dB at
the mouth of the horn, and using AU-60 it was 118 dB.
The SPL output using AU-60 at 1 m above the horn mouth with respect to the input
electrical power is plotted in Fig. 3. The radiation pattern of the horn with Ahuja AU-60
was measured as shown in Fig. 4. The 3 dB beamwidth is about 40◦ and emitted level
towards the horizon is about 20 dB below that in the vertical direction. A relatively narrow beam is useful in directing major portion of the energy towards vertical direction
and is preferable as the atmospheric attenuation at around 3 kHz is severe. High level
of atmospheric attenuation limits the range coverage of the RASS. Use of high power
transmitter would be intuitively more suitable for better range coverage performance.
But preliminary results showed that the maximum range coverage was about similar
with either of these transmitters. Though it needs further investigation, limitations due
to the background wind field seem to dominate the range coverage performance of
RASS. Distortion of the acoustic wavefronts due to turbulence is an additional contributing factor. It has been analytically shown that the range coverage performance
of a RASS depends on the background wind conditions and turbulence (Clifford and
Wang, 1977; Lataitis, 1992). Masuda (1988) has formulated an analytical framework
based on acoustic ray-tracing to find out the optimum beam direction for maximum
range coverage.
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3.1 Observation scheme of LAWP
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Using the LAWP-RASS, a preliminary experiment was conducted. The experiment was
started with the high power exciter at around 09:30 LT on 27 August 2010. However, the
high power exciters failed probably due to thermal heating as they are mounted on top
and the rain protection cover (not shown in Fig. 2) did not allow heat dissipation. Then
the system was switched to use the AU-60 exciter and the experiment was restarted
at around 17:20 LT on 27 August 2010. The experiment continued until about 03:00 LT
on 28 August 2010 and stopped due to failure of power amplifier. The power amplifier
was replaced and the experiment was restarted around 13:00 LT on 28 August 2010
and was continued up to 13:00 LT on 30 August 2010.
The specifications of the experiment with LAWP-RASS are shown in Table 2. The
acoustic source was swept between 3003 Hz and 2929 Hz corresponding to temperatures of 35 ◦ C and 20 ◦ C, respectively. In this experiment four modes of operation were
carried out viz., RASS mode 1, correction wind mode, background wind mode and
RASS mode 2. In the present wind profiler system, there is provision to run only up to
a maximum of four experimental specifications sequentially. The RASS mode 1 is that
for measuring the line of sight speed of acoustic wavefronts. Correction wind mode 1
is intended to record the line of sight wind speed and use it to correct the apparent
speed recorded in RASS mode 1. Background wind mode 1 is intended for recording
the three-dimensional wind field. In these three modes, the lowest range from which
recording can start is 300 m and the range resolution is 150 m corresponding to 1 µs
transmission.
To extend the lowest height of observation below 300 m, a fine range resolution mode
viz., RASS mode 2 was tested. In this mode the pulse width of transmission is 0.25 µs
and the corresponding range resolution is 37.5 m. Due to the current limitation of the
number of specifications being run in a sequence, correction wind mode of the second rass mode could not be conducted. It would be possible to use the three-beam
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3 Coordinated RASS observations with LAWP and MST radars
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observation from a colocated SODAR (Anandan et al., 2008) but as the data was not
reliable above 150 m it could not be used.
Figure 5a–d shows typical spectra in respectively the RASS mode 1, correction wind
mode 1, RASS mode 2 and background wind mode 1. Figure 5a shows the range coverage of the 1 µs operation with LAWP-RASS. The RASS echo was obtained up to
1.2 km. The maximum height coverage with both high power system and lower power
system is similar; better SNR resulted when using the higher power system. This preliminary result indicates that height coverage is limited by the background wind conditions at surface and aloft. Figure 5d shows the coverage with 0.25 µs pulse operation.
The lowest range from which signal is available is around 200 m and the maximum
height reached is about 800 m. The lowest heights below 200 m do not have any signal. This could be due to the separation between the antenna array and the acoustic
source. Due to the nature of the LAWP antenna, acoustic source cannot be kept at the
center of the antenna array. However, if the acoustic sources can be accommodated
into the antenna by appropriate design it would be useful to obtain echoes from the
lowest height possible. The lowest height in a monostatic radar is limited by the T/R
switch recovery time and the antenna size (which determines the distance to the far
field).
The Doppler spectra were subjected to moments computation by fitting a Gaussian
curve to the individual spectra in each range bin. The mean Doppler of RASS echo so
computed needs correction by subtracting the Doppler shift of the turbulence echo in
the same beam direction to obtain the Doppler shift due to the true sound speed. However, as the 1280 MHz frequency is highly sensitive to precipitation leading to stronger
echoes, the turbulence Doppler spectrum in the lower ranges, at which RASS echo
was obtained, is contaminated. As a result, the retrieved Doppler is in error. Therefore
correcting the RASS apparent Doppler shift in this method was not feasible. A solution
was found in the way the experiment was done. It is noted that RASS observation was
◦
done along five beams, viz., one zenith and four 5 off zenith in E, W, N and S directions. As the atmospheric motions are homogeneous over the cone of volume covered
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4 Results and discussion
4.1 Background meteorological conditions
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During this experiment, the sky was mostly cloudy and visual observations during daylight hours showed many specks of cloud moving with the wind over the wind profiler
site at a very low altitude of about 200 m. Further, there were occasional rain showers. Pictures from an onsite all sky imager showed an overcast sky with occasional
clearings on the morning of 27 and 28 August.
An onsite 50 m tower recorded the temperature, humidity, wind speed and direction
at six levels above ground at 2, 4, 8, 16, 32 and 50 m. Rainfall and surface pressure
were also recorded. Figure 6a shows the plots of virtual temperature at all the levels.
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During this experiment MST radar RASS was also operated along with the wind
profiler-RASS on 27–30 August 2010. Experimental specifications used for MST radarRASS are shown in Table 3. The corresponding acoustic sources generated swept
frequency waveform in the range 125 Hz to 94 Hz corresponding to temperatures of
◦
◦
−90 C and 40 C, respectively. An example of typical spectra from MST radar-RASS
can be found in Chandrasekhar Sarma et al. (2011).
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by the wind profiler beams, when vertical wind is neglected, the line of sight Doppler
shifts due to turbulence along coplanar beams symmetrical about the zenith would be
same in absolute values only with signs being opposite. Using this method the Doppler
shift due to the acoustic speed was computed by averaging the observed Doppler shifts
in symmetrical beams, viz., E and W and N and S wherever RASS echo was present.
Such a facility was not available in the 0.25 µs observation as the echo was not present
in the recordings of all the symmetric beam directions.
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4.2 Continuous temperature profile between 0.5 and 10 km altitude on
27 August 2010
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From Fig. 9a and b, we see that the effect of diurnal variation of ground temperature as
illustrated by data from 50 m tower (shown in Fig. 6a) is evident in the diurnal variation
of Tv at heights up to 900 m. Such a phenomenon can also be seen at the lowest height
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4.3 Diurnal variations of the temperature
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Figure 7 shows a colour coded plot of Tv profiles obtained during 27–30 August 2010
using MST radar for about 72 h. The height coverage of the Tv retrieval reached up
to 12 km in altitude on the first day. However, later on due to changes in the wind
field, failure of some acoustic exciters and rainfall, acoustic echo was missing. When
the acoustic echo was present during rainfall, the wind Doppler spectrum was contaminated and Tv retrieval was unstable. In order to enhance the visual perception of diurnal
temperature variation at lower tropospheric altitudes, Tv profiles are shown only up to
5 km in Fig. 7.
Figure 8a shows the colour coded plot of Tv retrievals from 1 µs observations of
LAWP-RASS. It shows that most of the time the Tv retrieval was only up to 750 m
altitude. This is because, even though acoustic echo was available up to about 1.0 km,
due to absence of echo in the symmetric beam directions, retrieval could not be done.
The Tv retrievals from 0.25 µs observation are shown Fig. 8b as a colour coded plot. The
height coverage of the 0.25 µs reached up to about 800 m. With the addition of LAWPRASS, the temperature profiling capability at NARL has been extended from ground
to above the tropopause. Figure 9a shows a stackplot of the Tv from 1 µs observations
shown in Fig. 8a. Similarly, Fig. 9b shows a stackplot of Tv from the 0.25 µs observation
shown in Fig. 8b.
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Figure 6b shows the rain rate. Simultaneous TRMM-TOVAS satellite observations also
revealed presence of scattered precipitation over the region of peninsular India.
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We present the application of RASS technique to a UHF (1280 MHz) wind profiler. The
wind profiler-RASS was operated in two modes. One with standard resolution of 150 m
and another with a finer resolution of 37.5 m. The former mode covered the range from
450 m to 1.2 km. The latter mode covered the lower heights starting at about 200 m up
to ∼800 m. Due to the problem of contamination of turbulence Doppler spectra by hydrometeors, the RASS acoustic Doppler frequency obtained in symmetrical beams was
used to correct for the effect of background wind. The error introduced in temperature
measurement is limited to the effect of vertical wind speed.
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in the MST Radar RASS observations shown in Fig. 7. The periodogram analysis of the
Tv profiles shows that the maxima in the temperature occur around 14:00 LT at lower
heights whereas they are progressively delayed as altitude increases. The amplitudes
of the diurnal temperature variation due to surface heating also decrease with altitude. The maximum virtual temperatures at heights of 2 m, 8 m and 50 m occur around
14:00 LT. These values on 28th August are respectively 37 ◦ C, 36.3 ◦ C and 35.3 ◦ C, re◦
◦
◦
spectively and on 29 August they are 35 C, 34.6 C and 33.6 C, respectively. From
the virtual temperatures derived using 0.25 µs pulse transmission data of 29 August,
maxima at heights 262.5 m, 300 m, 337.5 m, 375 m, 412.5 m, 450 m, 487.5 m, 525 m,
562.5 m, 600 m occur respectively at 19:36 LT, 19:17 LT, 19:27 LT, 19:23 LT, 19:41 LT,
19:51 LT, 20:27 LT, 20:27 LT, 20:42 LT, 20:30 LT. The temperature maxima are respec◦
◦
◦
◦
◦
◦
◦
◦
tively 31.09 C, 31.28 C, 31.16 C, 31.15 C, 31.09 C, 30.98 C, 30.54 C, 30.53 C
◦
◦
30.41 C, 30.49 C. This phenomenon delineates the boundary layer from the free troposphere. Using the Tv data the height of the boundary layer could be clearly delineated. Usually the boundary layer height extends up to about 3.5 km at Gadanki. However, as this preliminary experiment was conducted on an overcast day, signatures of
boundary layer height could be discerned only up to the lowest range bins of MST
radar-RASS observations viz., up to about 2.5 km.
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Anandan, V. K., Kumar, M. S., and Rao, I. S.: First results of experimental tests of the newly developed NARL phased-array Doppler Sodar, J. Atmos. Ocean. Tech., 25, 1778–1784, 2008.
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Angevine, W. M., Bakwin, P. S., and Davis, K. J.: Wind profiler and RASS measurements compared with measurements from a 450-m-tall tower, J. Atmos. Ocean. Tech., 15, 818–825,
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Chandrasekhar Sarma, T. V., Narayana Rao, D., Furumoto, J., and Tsuda, T.: Development
of radio acoustic sounding system (RASS) with Gadanki MST radar – first results, Ann.
Geophys., 26, 2531–2542, doi:10.5194/angeo-26-2531-2008, 2008.
Chandrasekhar Sarma, T. V., Kodama, Y.-M., and Tsuda, T.: Characteristics of atmospheric
waves observed in the upper troposphere observed with the Gadanki MST radar-RASS, J.
Atmos. Sol.-Terr. Phys., 73, 1020–1030, 2011.
Clifford, S. and Wang, T.: The range limitation on radar-acoustic sounding systems (RASS) due
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Acknowledgements. National Atmospheric Research Laboratory is a grants-in-aid institution
of the Department of Space, Government of India. The first author acknowledges the support
from Atmospheric Science Programme office of Department of Space by way of funding for
the RASS project. He also acknowledges the financial support by Japan Society for Promotion
of Science to cover research trips to Japan by way of Ronpaku fellowship during the financial
years 2006–2010.
Discussion Paper
Data obtained from the operation of the LAWP-RASS along with data from 50 m
tower and MST-Radar RASS extended the height coverage of temperature profiling from near ground up to upper tropospheric heights and potentially beyond the
tropopause.
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Sarma et al.
Title Page
Abstract
Introduction
Conclusions
References
Tables
Figures
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Furger, M., Whiteman, C. D., and Wilczak, J. M.: Uncertainty of boundary layer heat budgets
computed from wind profiler-RASS networks, Mon. Weather Rev., 123, 790–799, 1995.
Lataitis, R. J.: Signal power for radio acoustic sounding of temperature: the effects of horizontal
winds, turbulence, and vertical temperature gradients, Radio Sci., 27, 369–385, 1992.
Masuda, Y.: Influence of wind and temperature on the height limit of a radio acoustic sounding
system, Radio Sci., 23, 647–654, 1988.
May, P. T.: Thermodynamic and vertical velocity structure of two gust fronts observed with
a wind profiler/RASS during MCTEX, Mon. Weather Rev., 127, 1796–1807, 1999.
May, P. T. and Wilczak, J. M.: Diurnal and seasonal variations of boundary-layer structure observed with a radar wind profiler and RASS, Mon. Weather Rev., 121, 673–682, 1993.
May, P. T., Strauch, R. G., Moran, K. P., and Ecklund, W. L.: Temperature sounding by RASS
with wind profiler radars: a preliminary study, IEEE T. Geosci. Remote Sens., 28, 19–28,
1990.
Srinivasulu, P., Padhy, M. R., Yasodha, P., and Narayana Rao, T.: Development of UHF Wind
Profiling Radar for Lower Atmospheric Research Applications: Preliminary Design Report,
National Atmospheric Research Laboratory, Gadanki, India, 2006.
Srinivasulu, P., Yasodha, P., Jayaraman, A., Reddy, S. N., and Satyanarayana, S.: Simplified
active array L-band radar for atmospheric wind profiling: initial results, J. Atmos. Ocean Tech.,
28, 1436–1447, 2011.
Srinivasulu, P., Yasodha, P., Reddy, S. N., Kamaraj, P., Narayana Rao, T., Satyanarayana, S.,
and Jayaraman, A.: 1280 MHz active array radar wind profiler for lower atmosphere: system
description and data validation, J. Atmos. Ocean. Tech., doi:10.1175/JTECH-D-12-00030.1,
in press, 2012.
Westwater, E. R., Han, Y., Irisov, V. G., Leuskiy, V., Kadygrov, E. N., and Viazankin, S. A.:
Remote sensing of boundary layer temperature profiles by a scanning 5-mm microwave radiometer and RASS: comparison experiments, J. Atmos. Ocean. Tech., 16, 805–818, 1999.
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Discussion Paper
Table 1. Specifications of the 16 × 16 lower atmospheric wind profiler at Gadanki.
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Antenna beam width
Beam former
Beams directions
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Tx/Rx type
Peak power
Duty ratio
Pulse width
NCI
NFFT
Range bins
Receiver
Dynamic range
Minimum height
5, 4447–4472, 2012
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T. V. Chandrasekhar
Sarma et al.
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1280 MHz
256 element microstrip patch array arranged
in a 16 × 16 matrix of size 2.8 m × 2.8 m
◦
5
Passive (Modified Butler Matrix)
Five [(11◦ , 15◦ ), (101◦ , 15◦ ), (0◦ , 0◦ ), (191◦ ,
15◦ ) and (281◦ , 15◦ )]
Solid state transceivers
1.2 kW
Up to 10 %
0.25 µs–8.0 µs
4–1000
32–1024
1–256
Super heterodyne
70 dB
112.5 m
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Frequency
Antenna type
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Specification
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Parameter
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Table 2. Experimental parameters of LAWP-RASS operation.
Background
wind mode 1
RASS
mode 2
Pulse Width (µs)
Range resolution (m)
Inter Pulse Period (µs)
Beam sequence
1.0
150
55
◦
◦
E5 , W5 ,
◦
Z, N5 , S5◦
32
512
20
300 m
40
−3000 Hz
∼2.0 min
1.0
150
55
◦
◦
E5 , W5 ,
◦
Z, N5 , S5◦
256
256
10
300 m
40
0 Hz
∼3.0 min
1.0
150
55
◦
◦
E15 , W15 ,
◦
Z, N15 , S15◦
32
512
20
300 m
40
0 Hz
∼1.0 min
0.25
37.5
25
◦
◦
E5 , W5 ,
◦
Z, N5 ,S5◦
32
1024
20
112.5 m
55
−3000 Hz
∼1.5 min
No. of coherent integrations
No. of FFT points
No. of online incoherent integrations
Start of observation range window
No. of range bins
Second LO offset frequency
Time duration
3003 Hz to 2929 Hz
5 s ON, 1 s OFF
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Observation of
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T. V. Chandrasekhar
Sarma et al.
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Acoustic frequency sweep range
Acoustic excitation duty
Discussion Paper
Correction
wind mode 1
|
RASS
mode 1
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Parameter
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Table 3. Experimental specifications of MST-RASS operation.
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Background
wind mode
Pulse Width (µs)
Range resolution (m)
Inter Pulse Period (µs)
Beam sequence
1
150
250
Chosen based on
ray tracing result
96
256
8
1.5 km
160
−110 Hz
∼3.5 min
1
150
250
Same as in
RASS mode
128
256
8
1.5 km
160
0 Hz
∼4.5 min
1
150
250
E20◦ , W20◦ , Zy∗ ,
Zx∗ , N20◦ , S20◦
128
512
2
1.5 km
160
0 Hz
∼4 min
No. of coherent integrations
No. of FFT points
No. of online incoherent integrations
Start of observation range window
No. of range bins
Second LO offset frequency
Time duration
Zx and Zy – Zenith beams formed using N–S and E–W dipoles, respectively.
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∗
125 Hz to 94 Hz
4 s ON, 2 s OFF
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Observation of
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Acoustic frequency sweep range
Acoustic excitation duty
Discussion Paper
Correction
wind mode
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RASS
mode
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Parameter
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FIGURES
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(b)
Figure 1 : (a) The 64 element wind profiler with enclosure and antenna array on the top. (b) The
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Observation of
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T. V. Chandrasekhar
Sarma et al.
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Fig. 1. (a) The 64 element wind profiler with enclosure and antenna array on the top. (b) The
rooftop antenna
clutter fence
fence of
rooftop
antenna with
with clutter
of the
the 256
256element
elementwind
windprofiler
profileralong
alongwith
withacoustic
acousticexciters.
exciters.
Discussion Paper
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Abstract
Horn cross
section with
JBL2450H
mounted
on the top
its photograph.
dimensions
are
Fig. 2. (a) Horn cross
section
with
AU-60
mounted
atandthe
bottom All
and
its photographs.
(b) Horn
cross section within mm.
JBL2450H mounted on the top and its photograph. All dimensions are in
mm.
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4465
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(b)
Figure 2: (a) Horn cross section with AU-60 mounted at the bottom and its photographs. (b)
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T. V. Chandrasekhar
Sarma et al.
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Fig. 3. Input electrical power versus sound pressure level output of the horn using AU-60 driver.
Measurements were made 1 m above the mouth of the horn.
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T. V. Chandrasekhar
Sarma et al.
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Fig. 4. Radiation pattern of the Ahuja WFB horn with AU-60 compression driver.
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(b)
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(d)
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Figure 5 : Typical Doppler spectra obtained from WP-RASS. (a) acoustic echo with 1µs
Fig. 5. Typical Doppler spectra obtained from WP-RASS. (a) acoustic echo with 1 µs transmistransmission.
(b) 5º Turbulence
with 1 µs transmission;
acoustic
echoµs
with
0.25 µs
sion.
(b) 5◦ Turbulence
echo with 1echo
µs transmission;
(c) acoustic(c)
echo
with 0.25
transmission;
◦
(d)
15
turbulence
echo
with
1
µs
transmission.
transmission ; (d) 15º Turbulence echo with 1 µs transmission.
5, 4447–4472, 2012
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Abstract
Fig. 6. (a) Virtual temperature at the six levels of the 50 m tower; (b) rainrate measured near
the 50 m tower.
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4469
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(b)
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5, 4447–4472, 2012
Observation of
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T. V. Chandrasekhar
Sarma et al.
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gure 7Fig.
: The
Tv Tobservations
using MST radar -RASS starting at 12:54 LT on 27 August
7. The
v observations using MST radar-RASS starting at 12:54 LT on 27 August 2010 and
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on upto 13:30 LT on 30 August 2010.
10 andgoing
going
on upto 13:30 LT on 30 August 2010.
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Abstract
Fig. 8. (a) Colour coded plot of Tv observations using 1 µs operation of WP-RASS; (b) colour
coded plot of Tv observations using 0.25 µs operation of WP-RASS.
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4471
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T. V. Chandrasekhar
Sarma et al.
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Abstract
Fig. 9. (a) Line plot of the time series of virtual temperature using 1 µs observation; (b) line plot
of the time series of virtual temperature using 0.25 µs observation.
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Observation of temperature profiles by RASS

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